1. Field
The present invention relates to a method of cutting or separating a sheet of glass from a moving ribbon of glass, and in particular, ensuring a stable orientation of the ribbon during the separating cycle by compensating for a varying weight of the glass ribbon.
2. Technical Background
Down draw processes like the fusion-draw process produce a continuous ribbon of glass that transitions from a viscous glass-forming material to an elastic solid as the glass descends from a forming body. As the length of the glass ribbon grows, a point is reached when a cutting apparatus cuts (separates) a glass sheet from the ribbon, thereby shortening the ribbon by the length of the glass sheet. In addition to shortening the ribbon, the weight of the ribbon decreases by the weight of the separated glass sheet.
In a typical downdraw process used to produce glass sheets used in the manufacture of display panels, it is important to minimize contact between portions of the ribbon that will form a part of the subsequent display panel, the so-called quality area of the ribbon. Consequently, contact is sparing, and performed typically only at the edges of the ribbon, which are later removed. Therefore, the glass ribbon is only moderately constrained by the drawing apparatus. More particularly, the free end of the ribbon, from which the glass sheet is removed, is freely hanging from upstream supports when not engaged by the cutting apparatus. When a glass sheet is cut from the free end of the ribbon, the sudden reduction in weight that occurs when the glass sheet is removed can cause the newly formed free end to spring into a new shape. This sudden change in shape can be propagated upstream through the ribbon and perturb the drawing process. For example, the pulling force on the ribbon produced by upstream pulling rolls can be disrupted, and stresses can be induced into the glass ribbon as the glass ribbon transitions from a viscous liquid to a solid as it passes through the glass transition temperature range. A method and apparatus that compensates for the change in weight of the ribbon would minimize or eliminate this source of process inconsistency.